During weaving on a weaving loom, a shed is in each case formed between warp threads during successive weaving cycles and one or more weft threads are inserted between these warp threads by a respective weft-insertion device, following which the newly inserted yarn is beaten up against the previous weft thread in the fabric being produced. Each weft-insertion device comprises for example a pair of cooperating rapiers consisting of a giver rapier and a taker rapier which, in each weaving cycle, first simultaneously move towards each other from a respective side of the weaving loom in the shed until they meet and then perform a return movement until they have withdrawn from the shed. In this case, the giver rapier inserts the end of the weft yarn from one side into the shed so that it can be transferred to the taker rapier in the shed and this taker rapier then takes the yarn end to the other side, so that a length of the weft yarn eventually stretches from one side to the other side through the shed.
Each giver rapier comprises means to hold the yarn so that it is carried along during the rapier movements. These may be, for example, clamping means or a catch space or a slot or a combination of one or more such means, generally denoted by the term catch means.
After such a yarn insertion, the inserted yarn is still connected to the yarn stock and the inserted length of yarn has to be cut from the weft yarn stock before the next yarn can be inserted. Furthermore, the free end of the weft yarn also has to be inserted correctly in said catch means of the rapier, so that the weft yarn is ready to be inserted in the shed during a subsequent weaving cycle.
It is known to provide a rapier weaving loom for weaving flat fabrics with a device for detaining and cutting off weft yarn having the characteristics described in the first paragraph of this description. More particularly, the device consists of a fixed clamping surface and an elongate elastically deformable clamping body which is fixedly attached opposite the clamping surface. A weft yarn can be clamped between the clamping surface and the clamping body as a result of the resilient action of the clamping body.
This known arrangement is configured in such a way that when the giver rapier moves towards the fabric for a next yarn insertion, this rapier carries along the weft yarn to be cut which extends between the fabric edge and the yarn stock and positions it between the resilient clamping body and the clamping surface, so that it is clamped. Since the giver rapier meanwhile moves further towards the shed with respect to the clamped weft yarn, the yarn will be pulled into the catch means of the rapier. As a result of the rapier moving further along, an increasing tensile force is exerted on the clamped yarn, as a result of which the weft yarn is eventually pulled out of the clamp and is moved further by the giver rapier until it comes within range of the cutting device and is finally cut between the fabric edge and the rapier. The giver rapier now holds the end of the weft yarn in its catch means and is ready for a subsequent yarn insertion.
This device has the drawback that the length of the elastically deformable clamping body is relatively large, as a result of which it takes up a considerable amount of space on the weaving loom. Consequently, this device is not suitable for use on a double-face weaving loom with two or more rapier devices operating one above the other. After all, the device also has to be arranged as closely as possible to the fabric edge in order to prevent too much weft yarn from being lost in the thread ends which protrude at the fabric edge and which are subsequently removed as waste. In the limited intermediate space between rapiers operating one above the other, it is not possible to provide a space for this bulky device which limits the loss of yarn.
Another drawback is that the clamping force of such a resilient clamping body shows relatively significant variations, depending on the properties (e.g. the thickness) of the yarn, and cannot be controlled, or at least not accurately. As a result thereof, the tensile force at which the yarn will break free from the clamp varies. However, with a view to the reliability of this device, the yarn should always be released and cut at virtually the same tensile force.
Belgian patent BE 1014135A3 describes a device which automatically cuts weft threads and which then picks up the free thread ends on the fabric edge and presents them to two rapiers of a double-face weaving loom which operate one above the other. Picking up and presenting weft yarn by means of yarn clamps on rotatable presentation levers requires complex drives and control units.